Various kinds of Babesia species can infect dogs, and the most common ones are Babesia canis (also called large Babesia) and Babesia gibsoni (also called small Babesia). Babesia gibsoni is mainly distributed in Asia, including Japan, Korea, Taiwan and Malaysia. It is now also recognized as being widely distributed in Africa, Middle East, Brazil, North America, and Australia. Babesia gibsoni is an intraerythrocytic apicomplexan parasite that causes piroplasmosis in dogs. This disease is mainly transmitted naturally by ticks, but many reports have demonstrated transmission by dog bites and blood transfusions and transmission via the route to the developing fetus. Babesia gibsoni infection occurs frequently in dogs, and recently has become a serious problem from a clinical viewpoint, because the acute form of the disease typically results in serious clinical problems, such as fever, thrombocytopenia, regenerative anemia, splenomegaly, and sometimes death. Furthermore, infected animals may become chronic carriers and transmit the disease via ticks to other animals. Therefore, in order to control Babesia gibsoni infection, rapid and accurate diagnosis followed by prompt effective treatment, and the prevention of chronic carriers are needed.
Since the therapeutic approaches for Babesia canis and Babesia gibsoni are different, it is important to rapidly and correctly diagnose Babesia gibsoni to avoid inadequate treatment. However, Babesia gibsoni is not easy to be diagnosed. Generally, the methods employed for Babesia gibsoni diagnosis include blood smear, serologic diagnosis and molecular diagnosis, but each method has some limitations.
A veterinarian may perform direct pathogen detection in blood smears stained by Giemsa, but it is hard to differentiate large and small Babesia species in stained blood smears. This method significantly depends for its accuracy on well-trained and experienced technologists. Besides, this method requires fresh samples to preserve organism viability and morphology, and thus the samples must be processed very quickly.
Serologic diagnosis may be helpful in identifying the presence of antibodies to Babesia gibsoni, but serology cannot distinguish between animals with an acute or chronic infection. The limitations of serologic diagnosis are cross-reactions (especially between different Babesia species), which results in reduced specificity, and false-negative findings in young or immunosuppressed dogs, or early in the course of infection before seroconversion has occurred.
One of the current and workable way to diagnose Babesia gibsoni is molecular diagnosis, especially by polymerase chain reaction (PCR) testing. PCR, which is more sensitive and specific technique, offers an alternative approach for the diagnosis of babesiosis. An 18S rRNA gene sequence has been helpful in identifying species of Babesia and related protozoa. For example, the canine babesiosis 18S ribosomal RNA (18S) gene genesig standard kit provided by Primerdesign Ltd. is used to diagnose canine babesiosis. However, this kit cannot differentiate Babesia canis (large Babesia) and Babesia gibsoni (small Babesia).
Thus, there is a need of providing a method of specifically detecting Babesia gibsoni in order to select an appropriate treatment.